1. Field of the Invention
The invention relates to method of moulding a ceramic insulator for a spark plug structure in use for an internal combustion engine, and particularly concerns to an improved press for moulding granular or powdery materials by compaction.
2. Description of Prior Art
In moulding a ceramic insulator 100, binder agent and auxiliary sintering agent are added to ceramic powder to form a spray powder 110 as seen in FIG. 9. The spray powder 110 thus formed, is compacted into bullet shape configuration 120 by press. Then, the compacted ceramic is shaped by means of honing, and sintered.
However, the prior art has disadvantages as follows:
(A) An outer layer of high good density portion of the ceramic insulator is shaped, thus deteriorating the granular spray to impede reduction of numbers of blow holes, leading to lowering perforation voltage.
(B) Due to the shaping, a great quantity of non-reusable chips insulator costly.
(C) The shaping only allows a rotary body, thus restricting designing degree of freedom.
Therefore, it is an object of this invention to provide method of mould a ceramic insulator of a spark plug structure which is capable of determining a relatively high perforation voltage with minimum cost and high designing degree of freedom.
According to the present invention, there is provided method of moulding a ceramic insulator of a spark plug structure comprising steps of; making granular or powdery materials by mixing ceramic powder such as (AlN), (Si.sub.3 N.sub.4) or (Al.sub.2 O.sub.3) with an organic binder and an auxiliary sintering agent, so that average spherical diameter of the mixed powder falls within 20-100 microns; forcing the mixed ceramic into a mould, and pressed in an appropriate configuration; the ceramic thus pressed being sintered under normal pressure at the temperature of 1600-2000 degrees centigrade.
According to the present invention, cutting operation is eliminated at the time of shaping the ceramic insulator. This enables to remain an outer layer of the ceramic insulator to lower the number of blow holes so as to produce high density insulator with a high perforation voltage ensured.
No cutting chips are produced to reduce number of manufacturing processes to contribute to cost-saving.
Moulding according to the method allows not only rotary body but non-rotary body to ensure a high designing degree of freedom.
According, further, to the method of the present invention, the ceramic insulator includes a front half piece made of aluminum nitride (AlN) and a rear half piece made of alumina (Al.sub.2 O.sub.3), the two pieces are bonded at their respective ends by means of mortise tenon joint.
This needs minimum quantity of expensive aluminum nitride (AlN) to lead to cost-saving, and thermal shock resistance.
The mortise tenon joint allows to strengthen the bond between the front and rear half pieces by compression force and transverse direction stress when the ceramic insulator gets a high temperature.
Various other objects and advantages to be obtained by the present invention will appear in the following description and in the accompanying drawings.